1. Field of the Invention
The present invention relates to a shielded bearing provided with a shielding plate, and more particularly to a shielded ball bearing in which the shielding plate is molded into one piece from a polyacetal alloy resin.
2. Description of the Prior Art
It is well known to provide a shielding plate in a ball bearing in which a plurality of ball are interposed between an inner race and an outer race, and protected from dust by means of such shielding plate.
A conventional shielding plate is made of metals, or constructed of a metallic core plate with which a synthetic sealing rubber is molded to cover the core plate.
In case of the conventional shielding plate made of metals, the shielding plate is mounted on the outer race of the ball bearing and held therein by a snap ring having an appropriate resiliency. Consequently, in this case, two kinds of metals, i.e., one for the shielding plate and the other for the snap ring, are required, which increases manufacturing costs as to materials.
Further, in assembling, the snap ring snaps into an annular groove (which is formed in an inner surface of the outer race) to cause the outer race to vary in outer diameter. Such variation in outer diameter is particularly large in a miniature bearing which is considerably affected in dimension by the snap ring.
In addition, the outer race is required to have a pair of inner annular grooves, i.e., one For the shielding plate and the other for the snap ring. Due to this, the shield plate requires two steps in its assembling process, which increases the manufacturing cost of the ball bearing and causes many problems.
In a manufacturing process of the shielding plate constructed of the metallic core plate with which the synthetic sealing rubber is molded to cover the core plate, the core plate for providing the rigidity is previously press-formed; then, the synthetic rubber is placed on the core plate and subjected to heat and pressures, so that the rubber is molded to cover the core plate; and, thereafter, the thus molded rubber covering the core plate is blanked with a press to form the shielding plate. As is clear from the above, the manufacturing process of the shielding plate has many steps, and, is therefore costly.